Question: What did Danny DeVito eat instead of a raw fish during the scene where Shreck pushes the Penguin to run for mayor?
Question: Why is Penguin's blood green?
Answer: It isn't. If you look at when he dies you will see that he has cuts on his face that are bleeding red. The blue liquid is more like a bile, probably similar to saliva.
What about when he emerges from the water and green blood comes out of his nose and then his mouth?
Chosen answer: It is part of the mutation that caused his peculiar appearance.
Answer: He was actually eating raw fish.
Do you have a source for that? It seems unlikely.
Danny DeVito has stated in interviews that he ate fresh real bluefish (think of it like bluefish sashimi minus the soy sauce, wasabi, and ponzu).
Super Grover ★
Why would you think it seems unlikely? Lots of people eat raw fish. As long as it's treated properly to kill off bacteria (usually by flash-freezing it), it's perfectly safe. Heck, I even eat raw fish all the time. You just have to make sure it's sashimi-grade. Getting some raw bluefish seems cheaper and faster than going through a whole hullabaloo making a fake prop and concoction for the scene.
TedStixon